1. Field of the Invention
This invention relates generally to processes for the removal and disposal of airborne contaminants, and particularly to processes for the removal and disposal of airborne contaminants in effluent air streams from paint booths and the like.
2. Description of the Prior Art
The effluent air stream from industrial paint booths and the like may contain a number of airborne contaminants. The constitution of these contaminants depends upon the particular paints and solvents which are utilized, but typically an array of both water insoluble and water soluble contaminants is present. Examples of water insoluble contaminants which might be present would include hexanes, heptanes, octanes, nonanes xylenes, naphthas, and mineral spirits. Examples of water soluble contaminants which might be present would include alcohols, ketones, esters, and ethers. Other contaminants may include water soluble but high boiling substances such as glycol ethers. Airborne particulate contaminants may also be present.
The Environmental Protection Agency of the United States government has mandated strict adherence to goverment clean air standards. These standards require the removal of solvents and other contaminants from the effluent streams from paint booths and the like prior to venting these streams to the atmosphere. Strict government standards also regulate liquid effluents, and therefore a process without liquid effluents is desirable.
It is desirable to avoid the excessive release of water vapor to the atmosphere. Large amounts of water vapor released to the atmosphere, in some climatic conditions, can cause steam plumes and ice formation in cold climates and rain in warm climates. Large amounts of vapor produced in a process cannot be efficiently stored should a process component break down. It is therefore necessary to have standby components on hand or shut down the process. It is also desirable of course to keep the operating costs of such a process to a minimum.
The presence of substances such as carbon oxides, sulphur, or chlorinated compounds in exiting gas streams may result in the release of acids into the atmosphere. It is therefore sometimes necessary to scrub the gas streams leaving the process to remove these components. It would be desirable to provide a process which can be readily adapted to remove these substances.
The auto industry in particular has had difficulty in meeting clean air objectives while avoiding excessive operating costs. The magnitude of painting processes in the auto industry, and particularly the spray painting processes, produce a very large air and contaminant flow which is difficult to economically treat by conventional processes. Higher operating costs must ultimately of course be passed along to the consumer.
The technology of unit operations capable of performing specific separation functions for most chemicals at commonly encountered operating conditions is well known in the chemical engineering art. The art has not heretofore known, however, a satisfactory process for removing airborne contaminants from the effluent air streams of paint booths and the like, and especially from the effluent air streams from spray paint booths of the sort used in the auto industry.